The present invention is directed to a current interrupter of the type employing a dielectric liquid supplied to the vicinity of arcing contacts upon opening to extinguish the arc.
In U.S. patent application Ser. No. 818,004, filed July 22, 1977, now abandoned and assigned to the assignee of the present application, there is described an interrupter system which employs a dielectric liquid such as sulfur hexafluoride (SF.sub.6) to extinguish the arc between the contacts. That application describes an apparatus which forces the dielectric liquid through a nozzle. Where liquid SF.sub.6 is used, the excellent dielectric properties of the relatively high-density liquid, and the like pressures generated in the arcing region allow for interruption of currents exceeding 100,000 amperes. The interrupter of application Ser. No. 818,004 includes an accumulator system for smoothing the pressure variations encountered in the interrupter during high current interruptions. The approach described allows for high pressures in the arcing region while eliminating the complex pressure maintaining systems used in the prior art, such as are described in Leeds et al, U.S. Pat. No. 3,150,245. Another interrupter in which a dielectric liquid is forced through a nozzle in the arcing region is described in U.S. patent application Ser. No. 826,382, filed Aug. 22, 1977, now abandoned and assigned to the assignee of the present application.
In interrupters which use a pump piston moving in a cylinder to drive the dielectric fluid into the arcing region, the pump cylinder must be refilled after the piston has been returned to its starting position to allow for subsequent interruptions. Use of external pressure reservoirs for refilling the pump cylinder with dielectric liquid is undesirable for several reasons. First, a liquid dielectric is relatively incompressible and the pressure developed in a pressurized reservoir will drop rapidly as the liquid exits the reservoir. Consequently, mechanical pumping or suitable adjacent gas reservoirs are required to maintain pressure. Second, the sliding seals, valves, and connections associated with a high-pressure reservoir are susceptible to leaks. Furthermore, any system employing a pressure differential using liquid SF.sub.6 presents the problem of freezing of the dielectric fluid as it is dumped into a region of lower pressure.
In one prior art patent, Fisher, U.S. Pat. No. 3,406,269, an interrupter is disclosed (in FIG. 5) in which arcing contacts are immersed in liquid SF.sub.6 and a separate pressure reservoir is not used. Fisher suggests, however, that the interior pressure of the interrupter be maintained at 2,000 p.s.i., which presents severe leakage problems requiring high cost construction techniques. The Fisher interrupter would be unable to successfully interrupt very large currents (100,000+ amperes) at lower interior pressures.